diff --git a/libc/include/sys/capability.h b/libc/include/sys/capability.h
index 4cb698f..b43bbf0 100644
--- a/libc/include/sys/capability.h
+++ b/libc/include/sys/capability.h
@@ -44,7 +44,7 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
-int capget(cap_user_header_t __hdr_ptr, cap_user_data_t __data_ptr);
+int capget(cap_user_header_t _Nonnull __hdr_ptr, cap_user_data_t _Nullable __data_ptr);
 
 /**
  * [capset(2)](http://man7.org/linux/man-pages/man2/capset.2.html) sets the calling
@@ -52,6 +52,6 @@
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
-int capset(cap_user_header_t __hdr_ptr, const cap_user_data_t __data_ptr);
+int capset(cap_user_header_t _Nonnull __hdr_ptr, const cap_user_data_t _Nullable __data_ptr);
 
 __END_DECLS